JP-56-14116A (U.S. Pat. No. 4,373,383), JP-63-117219A or JP-4-147016A describes an air flow rate measuring apparatus having heat-cleaning function using a heater.
In JP-56-14116A, a heat-cleaning is implemented when an engine is stopped so as not to affect an air-fuel ratio control of the engine. JP-56-14116A requires an external determination circuit in addition to the air flow rate measuring apparatus. The external determination circuit is a trigger circuit which determines whether the heat-cleaning should be implemented or not based on, for example, a start-and-stop number or a temperature of the engine. The heat-cleaning is implemented when an instruction signal for starting the heat-cleaning is sent to the air flow rate measuring apparatus from the external determination circuit.
Further, a dedicated harness is necessary for a connection between the external determination circuit and the air flow rate measuring apparatus. Thus, a cost of the configuration for implementing the heat-cleaning is increased.
Moreover, it is required that an electric power is supplied for a short time to the external determination circuit and the air flow rate measuring apparatus after the engine is stopped. Thus, a cost of the electric power is increased.
Furthermore, the heat-cleaning may be implemented even though a temperature of an intake air is high. If the heat-cleaning is implemented while the temperature of the intake air is high, a temperature of the heater is too much raised and the heater is deteriorated. In this case, a measuring accuracy of an air flow rate is lowered.
In JP-63-117219A, a heat-cleaning is implemented at a fuel-cut time when the engine is decelerated so as not to affect an air-fuel ratio control of the engine.
Because the heat-cleaning is implemented each time when the fuel-cut occurs, a deterioration of the heater is accelerated and a measuring accuracy of the air flow rate is lowered.
In JP-4-147016A, the air flow rate measuring apparatus has a heat-emitting resistor for a heat-cleaning, which is separate from a heater for measuring a flow rate.
Because the resistor is needed additionally to the heater, a configuration of the air flow rate measuring apparatus becomes complicated.